1. Field of the Invention
The present invention relates to a method for manufacturing a semiconductor device, and a semiconductor device that is obtained using such method, and a display device and an electronic device that includes such semiconductor device. More particularly, the present invention relates to a manufacturing method, wherein an aperture is formed in an insulating film provided on a substrate, and an amorphous silicon film is formed on such insulating film, and the amorphous silicon film is irradiated by a laser, so that a silicon film in a substantially single crystal state is formed in the position of the aperture, and a semiconductor device using such silicon film as a semiconductor film is produced.
2. Related Art
Conventionally, the method explained below has been used in the manufacture of a thin-film semiconductor device, typically a thin-film polycrystalline silicon transistor (p-Si TFT), in a low temperature condition, for example, at 600° C. or lower, that is, a temperature that permits the use of a general glass as a substrate, or at 425° C. or lower, that is, the same level of temperature as that at the time of the manufacture of an amorphous silicon thin-film transistor (a-Si TFT).
According to the forementioned method, a silicon dioxide film, which functions as an insulating film, is first deposited on the glass substrate as a base protecting film, and an amorphous silicon film, which will become a semiconductor film, is deposited on such silicon dioxide film. Subsequently, the amorphous silicon film is irradiated by an XeCI pulsed excimer laser beam (wavelength of 308 nm), thereby changing the amorphous silicon film into a polycrystalline silicon film (laser heat treatment process). In this laser heat treatment process, the amorphous silicon film absorbs the laser beam and is melted as its temperature rises, and the melted silicon film is crystallized as the temperature subsequently drops, and a polycrystalline silicon film is thus prepared.
After the laser heat treatment process, a silicon dioxide film, which will become a gate insulating film, is formed by the chemical vapor deposition method (CVD) or the physical vapor deposition method (PVD). Subsequently, a gate electrode made of tantalum or the like is formed, and a field effect transistor (MOS-FET) having a structure comprised of metal (gate electrode)—oxide film (gate insulating film)—semiconductor (polycrystalline silicon film) is obtained. Interlaying insulating films are deposited on these films, and after contact holes are formed, electrodes are wired using the thin metal film. Thus, a thin-film semiconductor device is completed.
However, according to such a method for manufacturing a thin-film semiconductor device, the energy density of the excimer laser beam is difficult to control, such that the energy density changes at the time of the laser heat treatment and results in wide variances of semiconductor film properties. These variances in the semiconductor film properties are particularly apparent around the laser irradiation states (irradiation energy densities) that enable the production of a relatively preferable polycrystalline semiconductor film. Therefore, in the actual manufacturing process, the energy density is set slightly lower than the optimum value in order to reduce the influence of such variances in the semiconductor film properties. However, by doing so, the energy density becomes insufficient, and the production of a preferable polycrystalline thin film becomes difficult.
Furthermore, even if a laser is irradiated with the optimum irradiation energy density that enables the production of a relatively preferable polycrystalline film, the silicon film is obtained in a polycrystalline state, and the grain boundaries of the polycrystal make the properties of the thin-film semiconductor device inferior to those made of single crystal silicon. Moreover, because the areas where the grain boundaries generate cannot be controlled, the properties of the thin-film semiconductor device formed on such polycrystalline silicon film widely vary in many cases, even in the same substrate.
The methods according to the “Single Crystal Thin Film Transistors,” IBM Technical Disclosure Bulletin, August 1993, pp 257-258, and the “Advanced Excimer-Laser Crystallization Techniques of Si Thin-Film For Location Control of Large Grain on Glass,” R. Ishihara et al., proc. SPIE 2001, vol. 4295, pp 14-23, intend to solve such drawbacks. These documents suggest a technology that includes the steps of: forming an aperture in an insulating film provided on a substrate; forming a silicon film on such insulating film; irradiating the silicon film with a laser beam under a prescribed condition; maintaining the silicon inside the bottom part of the aperture in an unmelted state while melting other parts of the amorphous silicon film; generating crystal growth using the unmelted silicon as a crystal nucleus; and changing the area around the aperture on the surface of the silicon film into a silicon film in a substantially single crystal state. A similar technology is also disclosed in Patent Laid-Open Publication No. SHO 62-119914.
According to the methods disclosed in these related art documents, the cross section of the aperture must be made sufficiently small to prevent the generation of a plurality of crystalline nuclei at the bottom part of the aperture. Therefore, an expensive and precise exposure device and etching device must be used to form the aperture. However, when a plurality of thin-film transistors are formed on a large glass substrate, such as a large liquid crystal display, it becomes difficult to form the aperture using these devices. The present invention intends to solve such drawbacks of the related art, and aims to provide a method that does not require the use of an expensive and precise exposure device or etching device to form the aperture in the insulating film.